In the pulp and paper industry, chip refining and pulp refining are two widely used processes that contribute significantly to the industry's energy costs. At the same time, these processes have a great impact on the factors of efficiency, productivity and end product quality. Improvement of each of these factors will naturally directly influence a producer's competitiveness.
There are two types of refining processes in use. Both types prepare the fibers for paper making. The processes change the fiber structure and paper making characteristics. The fiber walls are disrupted so that the fiber can collapse and become flexible. Also, fibrils in the fiber wall are freed to extend outward and engage with other fibers in the formed paper web. Some fibers are shortened in the refining process.
Pulp refiners take, as an input, pulp fibers in suspension after the fibers have been separated from each other in some prior process. One such prior process is chemical pulping.
Thermomechanical pulpers (TMP) have wood chips as an input. These refiners perform both the fiber separation process as well as preparing the fibers for subsequent processes.
In the U.S., the total annual energy consumption for pulp refining and chip refining are on the order of 180.times.10.sup.12 and 44.times.10.sup.12 BTU/yr, respectively. In a workshop entitled "Pulp And Paper Mill of the Future," sponsored by the U.S. Department of Energy in 1993, industry experts identified a number of critical technologies needed to improve energy efficiency, process efficiency, and waste reduction in the paper industry. In the area of refining, the technologies mentioned were advanced process control models based on fundamental studies, sensors to permit feedback control for power input, water and wood flow rates and angular velocity. In addition, it was noted that sensors to rate the quality of recycled raw materials would greatly facilitate the expanded use of this material.
A prevalent method of refiner control is through "specific energy," defined as horsepower days per ton (HPD/T). This control parameter is indicative of energy expended per unit material processed and is an approximate predictor of resultant pulp quality but is, of course, dependent upon efficiency. Another specific energy relationship is E=N.times.S, which has been known only in a theoretical way, where N represents the number of fiber impacts per unit time and S represents the severity (magnitude) of the impacts.
Previous attempts to measure both N and S independently, or to derive them from known parameters, have failed.